Current building construction techniques frequently call for the use of drywall sheets, otherwise called wallboard, to form the surfaces of interior walls. Sheets of drywall are made by encasing sheets of plaster with heavy construction paper. The paper provides extra strength and resistance to tearing and prevents crumbling of the enclosed plaster. The sheets of drywall are typically produced in sizes of four feet by eight feet to four feet by twelve feet. These sheets can be installed intact or can be cut to custom fit specific interior wall sizes. When cut, the inner plaster is exposed and is particularly vulnerable to crumbling or other damage unless the severed edges can be protected. An exposed corner, exterior or interior, formed by two interfacing drywall sheets not in the same plane is also susceptible to damage. Damage can be particularly severe when these corners involve cut or exposed edges. To overcome this vulnerability to damage and further reinforce exposed edges, particularly the exposed corner formed by two interfacing drywall sheets, a drywall trim such as a drywall corner bead will generally be installed at that corner. The corner being reinforced can be either an interior or exterior corner.
Two types of drywall trim are typically used in protecting exposed edges and reinforcing drywall corners—a paper-faced bead type (also known as a paperbead), and a solid all-metal or all plastic drywall trim type. Both the paperbead and the solid drywall trim typically include a strip of metal or plastic formed or extruded into a desired shape. One common example involves forming the metal or plastic strip into a core shape having two flanges and a center rib positioned between them. This form of drywall trim is called a rib-shape corner bead. Another common shape of drywall trim has two flanges and a larger curved portion or bullnose positioned between them. This shape of corner bead is called a bullnose corner bead. A third shape of drywall trim features an L-shape having one flange longer than the other and an offset rib between the flanges. Other common shapes of drywall trim include a J-shape, a splay-bead, and a shadow-mold.
Solid drywall trims such as a rib-shape corner bead are attached to drywall by driving nails, screws, staples or other fasteners through the flanges, securing the drywall trim with the heads of the fasteners to the underlying framing. A joint compound is then applied to cover the flanges and fastener heads. The compound is sanded and feathered to provide a smooth and continuous surface from the drywall surface to the center rib of the formed metal strip.
Paperbeads provide several advantages over solid drywall trims. For instance, both joint compound and paint adhere significantly better to the surface of a paperbead than to the exposed metal or plastic surface of a typical solid drywall trim. Moreover, paint applied directly to a metal or plastic surface is easily chipped after drying. Drywall corners covered with solid drywall trims are also more susceptible to cracking along the edges of the flanges. Thus, a paperbead provides a better surface for joint compound and paint adhesion and helps reduce plaster cracking.
Paperbeads differ from solid drywall trims in several respects. First, the paperbead has a paper strip attached to an outer surface of the formed metal or plastic core as previously discussed. Generally, portions of the paper strip extend beyond the edges of the metal or plastic core forming wings. The paperbead is attached to drywall by applying a joint compound to the drywall surface and embedding the formed metal strip and the paper wings in the compound. A second, exterior layer of joint compound is subsequently applied on top of the paperbead and allowed to dry. This exterior layer of joint compound is then sanded and feathered to form a smooth and continuous surface between the drywall and the corner bead. The steps of applying, sanding and feathering the exterior layer of joint compound can be repeated until a smooth surface is created. Throughout this process, the portion of the paper strip covering the core of the drywall trim, i.e. the center rib, the bullnose, or the offset rib, is left exposed or uncovered by joint compound.
The paper surface left exposed on a typical paperbead may be scuffed, or completely removed during the sanding and feathering process, thus exposing the metal surface of the core beneath. Scuffing makes it more difficult to later obtain a smooth painted surface at the paperbead because the paper becomes frayed or fuzzy. Also, as stated previously, paint does not adhere as easily to the exposed metal surfaces. Therefore, paint applied to any exposed metal surface will be more easily chipped after it dries. Moreover, a scuff in the paper surface produces a break in the line of the paperbead and reduces the aesthetic benefits of having such a bead.
To overcome the problems of scuffing, some paperbeads provide a surface coating at the exposed center portion of the paperbead to improve the paper's resistance to abrasion and avoid the problems caused by scuffing. This type of surface coated paperbead is disclosed in U.S. Pat. No. 5,131,198. A surface coating, however, only provides extra resistance to abrasion at the outer surface of the paper strip. If this coating is penetrated or removed by the sanding process, the underlying paper is exposed and is again made susceptible to scuffing. Consequently, the problems of paint adhesion, unsmooth surface finishes and, paint chipping are not avoided. Moreover, the application of a surface coating at a particular location involves an additional installation step thereby increasing the cost of installing the product.
To resolve the problem of surface coated paper, U.S. Pat. Nos. 5,836,122 and 5,613,335, both to Rennich et al., propose a paperbead for protecting drywall corners containing a paper strip bonded to a metal or plastic core. This paper strip is made of stock paper which is uniformly impregnated with latex throughout its thickness which imparts scuffing and abrasion resistance to the paper. However, such paperbead had problems with adhesiveness of the joint compound because of the latex coating on both surfaces of the paperbead.
Rennich et al, as described in U.S. Pat. No. 7,214,434, developed a paperbead with paper where one side of the paper had a strengthening compound penetrating into only a portion of the thickness of the paper, and the other side of the paper was roughened. This provided a paperbead which was resistant to abrasion and had excellent adhesiveness to joint compounds. The latex impregnated side of the paper maintained increased strength making the paper resistant to scuffing, while at the same time, the roughened side of the paper improved its adhesiveness to joint compounds.
It is not uncommon that the surface of drywall adjacent to its edge may have a significant non-planar contour, being rough, uneven, undulating or otherwise warped. These conditions may arise for example as a result of damage in handling or installing the drywall. For example, one or more drywall nails or screws attaching the drywall to the underlying framing may have been angled or recessed too far into the drywall or too close to the drywall edge, causing depressions and unevenness. There may be deformations due to drywall knife cuts, hammer strikes or other causes resulting in a non-planar contour of the surface of the drywall in a region adjacent or along the edge of the drywall. In conditions where the drywall surface has such non-planar contours, it has been found that there is a possibility of the prior art paperbeads not being able to properly follow and adhere to the non-planar surface of the drywall. This can give rise to the formation of bubbles or edge lifting of the paperbead.
While the above prior art arrangements have been successful in certain environments where the surface of the drywall panels have not been deformed, there is always a push to improve installed fit and finish, so there remains a need for a paperbead which can better follow non-planar contours of the drywall surface.